1. Field of Invention
The present invention relates to a driving method for an organic electro-luminescence display device, a driving method for an electro-optical device suitable for use with a display device, such as an organic electro-luminescence display device, an electro-optical device, and an electronic apparatus provided with such an electro-optical device.
2. Description of Related Art
Attention is being given to organic electro-luminescence display devices using organic materials as luminescent materials of luminescent elements since they have a wide viewing angle, and will potentially meet market demands, i.e., demands for thinner, lighter, smaller, and lower power-consuming display devices.
Unlike conventional liquid crystal display devices, in organic electro-luminescence display devices, a luminescence state of the luminescent element must be controlled by a current. One such control method is the conductance control method (T. Shimoda, M. Kimura, et al., Proc. Asia Display 98, 217; M. Kimura, et al., IEEE Trans. Ele. Dev. 46, 2282 (1999); M. Kimura, et al., Proc. IDW 99, 171; and M. Kimura et al., Dig. AM-LCD 2000, to be published). In this method, the luminescence state of the luminescent element is controlled by a current value, which is an analog value, and more specifically, it is controlled by changing the potential applied to a gate electrode of a driving transistor that drives the luminescent element. When thin-film transistors having different current characteristics are used, however, the difference in the current characteristics of the individual transistors may sometimes directly result in non-uniformity in the luminescence state of the luminescent elements.
Accordingly, the area ratio gray-scale method (M. Kimura, et al., Proc. Euro Display ""99 Late-News Papers, 71, Japanese Unexamined Patent Application Publication No. 9-233107, M. Kimura, et al., Proc. IDW 99,171, M. Kimura, et al, J. SID, to be published; and M. Kimura, et al., Dig. AM-LCD 2000 to be published) has been proposed. In the area ratio gray-scale method, unlike the above-mentioned conductance control method, the luminescence state of the luminescent elements is controlled without using a luminescence state at an intermediate luminance. More specifically, in this method, the gray-scale is displayed as follows. Pixels disposed in a matrix are divided into a plurality of sub-pixels, and it is determined whether the luminescent elements contained in the sub-pixels are either in a complete luminescence state or a complete non-luminescence state. Then, among the plurality of sub-pixels, the total area of the sub-pixels in the complete luminescence state is changed. In the area ratio gray-scale method, it is not necessary to set an intermediate current value corresponding to the luminescence state of the intermediate luminance. Accordingly, the influence of the current characteristics of the transistors that drives the luminescent elements can be reduced, thereby achieving a uniform image quality. In this method, however, the number of gray-scale levels is restricted by the number of sub-pixels. For a greater number of gray-scale levels, pixels must be divided into a greater number of sub-pixels, which makes the pixel structure complicated.
Accordingly, the time ratio gray-scale method (M. Kimura, et al., Proc. IDW 99, 171; M. Kimura, et al., Dig. AM-LCD 2000, to be published; M. Mizukami, et al., Dig. SID 2000, 912; and K. Inukai, et al., Dig. SID 2000,924) has been proposed. In the time ratio gray-scale method, the representation of the gray-scale is implemented by changing the period for which the luminescent elements in one frame are in the complete luminescence state. Accordingly, unlike the area ratio gray-scale method, it is not necessary to provide many sub-pixels for obtaining a greater number of gray-scale levels, and also, the time ratio gray-scale method can be used together with the area ratio gray-scale method. Thus, it is expected that the time ratio gray-scale method will be a promising method for digitally displaying a gray-scale.
However, in the SES (Simultaneous-Erasing-Scan) time ratio gray-scale method, which is reported in xe2x80x9cK. Inukai, et al., Dig. SID 2000,924xe2x80x9d, in addition to the scanning lines, reset lines are required, and thus, the luminescence area is disadvantageously reduced.
Accordingly, a first object of the present invention is to provide a method for implementing the representation of a gray-scale of an electro-optical device without reset lines, and in particular, to provide a method for implementing the representation of the gray-scale of an electro-optical device, such as an organic electro-luminescence display device, according to the time ratio gray-scale method. A second object of the present invention is to provide an electro-optical device that is driven by the above-described driving method.
In order to achieve the first object, a first driving method for an electro-optical device according to the present invention is a driving method for an electro-optical device which includes, at an intersection of a scanning line and a data line, an electro-optical element, a driving transistor that drives the electro-optical element, a switching transistor that controls the driving transistor, and a reset transistor that resets the driving transistor to a non-conducting state. The driving method includes: a setting step of supplying an on-signal to cause the switching transistor to be in an on-state to the switching transistor via the scanning line, and of supplying a set signal to select a conducting state or a non-conducting state of the driving transistor to the driving transistor via the data line and the switching transistor in accordance with a period for which the on-signal is supplied; and a resetting step of supplying an on-signal to cause the reset transistor to be in an on-state to the reset transistor via the scanning line so as to reset the driving transistor to the non-conducting state. Accordingly, by supplying the on-signal for the switching transistor and the on-signal for the reset transistor via the same scanning line, the luminescence period can suitably be set without a reset line. In this specification, the electro-optical element and the electro-optical device respectively indicate an element and a device in which the luminescence state or the optical characteristic is electrically controlled. Specific examples of the electro-optical device include display devices, such as luminescence display devices, liquid crystal display devices, and electrophoretic display devices.
Throughout the specification, the xe2x80x9cstep of supplying an on-signal to the switching transistor via the scanning line, and of supplying a set signal to select a conducting state or a non-conducting state of the driving transistor to the driving transistor via the data line and the switching transistor in accordance with the on-signalxe2x80x9d is defined as the xe2x80x9csetting stepxe2x80x9d. The xe2x80x9cstep of resetting the driving transistor to the non-conducting state by supplying an on-signal to cause the reset transistor to be in the on-state to the reset transistor via the scanning linexe2x80x9d is defined as the xe2x80x9cresetting stepxe2x80x9d.
According to a second driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the electro-optical device may further include a power line that supplies a current to the electro-optical element via the driving transistor, and one end of the reset transistor may be connected to the power line.
According to a third driving method for an electro-optical device of the present invention, the conductivity type of the switching transistor and the conductivity type of the reset transistor may be different from each other. More specifically, for example, if the switching transistor is n-type, the reset transistor is p-type. If the switching transistor is p-type, the reset transistor is n-type. Accordingly, by suitably selecting a high-potential signal or a low-potential signal, the switching transistor and the reset transistor can be complementarily operated.
According to a fourth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the conductivity types of the switching transistor, the driving transistor, and the reset transistor may be respectively n-type, p-type, and p-type. That is, when a high-potential scanning signal is supplied, the switching transistor enters the on-state. When a low-potential scanning signal is supplied, the reset transistor enters the on-state. Thus, the switching transistor and the reset transistor can be complementarily operated.
According to a fifth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, a voltage VS corresponding to the on-signal to cause the switching transistor to be in the on-state, a voltage VR corresponding to the on-signal to cause the reset transistor to be in the on-state, and a voltage V0 V0 corresponding to an off-signal to cause both the switching transistor and the reset transistor to be in an off-state may satisfy a relational expression: VS greater than V0 greater than VR.
According to a sixth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the voltage VS, the voltage VR, and the voltage V0 may satisfy relational expressions: xe2x88x92VS≈VR, and V0=0V (voltages). According to the driving methods for electro-optical devices set forth above, only by setting three voltage values, such as VS, V0, and VR, the on-off operation of the switching transistor and the on-off operation of the reset transistor can be performed.
According to a seventh driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, while the switching transistor is in the on-state, the reset transistor is in the off-state, and, while the reset transistor is in the on-state, the switching transistor is in the off-state. With this arrangement, the state of the electro-optical element and the period for which the selected state is retained can precisely be set.
According to an eighth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, a gray-scale may be obtained by setting a time interval between the setting step and the resetting step. That is, the time interval between the setting step and the resetting step corresponds to the period for which the selected state of the electro-optical element is retained. Thus, by suitably setting this time interval, a gray-scale can be obtained.
According to a ninth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, a gray-scale may be obtained by performing a plurality of set-reset operations, each set-reset operation including the setting step and the resetting step. In the setting step, the state of the electro-optical element is selected, and in the resetting step, the period for which the selected state is retained is determined. Thus, by repeating a plurality of above-described set-reset operations, a multi-level gray-scale can be obtained. Throughout this specification, the set-reset operation is defined as the operation including the setting step and the resetting step.
According to a tenth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the time interval between the setting step and the resetting step may be different for each of the plurality of set-reset operations.
According to an eleventh driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the time interval between the setting step and the resetting step for each of the plurality of set-reset operations may be completely different from the others, and the ratio of time intervals for the plurality of set-reset operations may be about 1:2: . . . :2n (n being an integer of one or more) based on the minimum time interval. For example, if two set-reset operations with a time interval ratio of 1:2 are performed, four gray-scale levels, i.e., 0, 1, 2, 3, can be displayed. If two set-reset operations with a time interval ratio of 1:1 are performed, three gray-scale levels, i.e., 0, 1, and 2 can be displayed. That is, in this driving method for an electro-optical device, a maximum number of gray-scale levels can be obtained by a minimum number of set-reset operations. The time interval ratio does not have to precisely be 1:2: . . . :2n (n being an integer of one or more), and may be sufficient to such a degree to satisfy a required gray-scale precision.
According to a twelfth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the set signal may be a signal to set the driving transistor to be in the conducting state rather than the signal to select the conducting state or the non-conducting state of the driving transistor. This means that an intermediate conducting state other than the two states, i.e., the conducting state and the non-conducting state, of the driving transistor is selectable. This can be implemented by supplying the set signal as a signal having three or more consecutive or discrete values. This driving method is effective to implement many gray-scale levels.
According to a thirteenth driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the electro-optical element may be an organic electro-luminescence element. The organic electro-luminescence element is a luminescent element using an organic material as an electric-field luminescent material.
A first electro-optical device of the present invention is driven by the above-described driving method for an electro-optical device. That is, in this electro-optical device, by supplying the on-signal for the switching transistor and the on-signal for the reset transistor via the same scanning line, the period for which the state of the electro-optical element selected in the setting step can suitably be set without a reset line.
A second electro-optical device of the present invention is an electro-optical device including, at an intersection of a scanning line and a data line, an electro-optical element, a driving transistor that drives the electro-optical element, a switching transistor that controls the driving transistor, and a reset transistor that resets the driving transistor to a non-conducting state. The electro-optical device includes at least one drive circuit that generates a signal to set the switching transistor and the reset transistor to be in an on-state or an off-state, and that generates a signal to set the driving transistor in accordance with the signal to set the switching transistor to be in the on-state. It is not essential that only the single drive circuit is used that xe2x80x9cgenerates a signal to set the switching transistor and the reset transistor to be in an on-state or an off-state, and that generates a signal to set the driving transistor in accordance with the signal for setting the switching transistor to be in the on-statexe2x80x9d. A plurality of drive circuits may be used.
A third electro-optical device of the present invention is an electro-optical device including, at an intersection of a scanning line and a data line, an electro-optical element, a driving transistor that drives the electro-optical element, a switching transistor that controls the driving transistor, and a reset transistor that resets the driving transistor to a non-conducting state. The electro-optical device includes: a scanning line driver that supplies a signal to set the switching transistor and the reset transistor to be in an on-state or an off-state to the scanning line; and a data line driver that supplies a signal to set the driving transistor to the data line in accordance with an operation of the scanning line driver.
A fourth electro-optical device of the present invention is an electro-optical device including, at an intersection of a scanning line and a data line, an electro-optical element, a driving transistor that drives the electro-optical element, a switching transistor that controls the driving transistor, and a reset transistor that resets the driving transistor to a non-conducting state. An on-signal that performs a setting step of setting a display condition of the electro-optical element is supplied to the switching transistor via the scanning line, and an on-signal that performs a resetting step of resetting a display condition of the electro-optical element is supplied to the reset transistor via the scanning line. In the above description, the definitions of the xe2x80x9csetting stepxe2x80x9d and the xe2x80x9cresetting stepxe2x80x9d are substantially similar to those of the setting step and the resetting step set forth previously above.
In the above-described electro-optical device, a fifth electro-optical device of the present invention may further include a power line that supplies a current to the electro-optical element via the driving transistor, and one end of the reset transistor may be connected to the power line. Accordingly, the first through fifth electro-optical devices of the present invention do not require a reset line that performs the time ratio gray-scale method. Advantageously, therefore, it is possible to ensure a sufficient display area. If more gray-scale levels are required, the time ratio gray-scale method can be employed with the area ratio gray-scale method by providing sub pixels in the pixels of the electro-optical device.
According to a sixth electro-optical device of the present invention, in the above-described electro-optical device, the electro-optical element may be an organic electro-luminescence element.
A first electronic apparatus of the present invention is an electronic apparatus in which the above-described electro-optical device is installed.